1. Field of the Invention
The present invention relates to a battery monitoring unit capable of monitoring, for example, the state of a battery pack constituted of a plurality of battery cells.
2. Description of the Related Art
An electric vehicle and a plug-in hybrid vehicle (PHV) have been put into practical use, and various types of vehicles have been brought to the market. In such vehicles, electric power is utilized as the source of power.
Such a vehicle is equipped with a storage battery, especially a battery pack (hereinafter, simply referred to as “battery”) constituted of a plurality of battery cells. Furthermore, a battery monitoring unit that controls and monitors the battery is provided to the vehicle. FIG. 1 illustrates a battery monitoring unit 101 having a conventional configuration. The battery monitoring unit 101 includes a control integrated circuit (IC) 100 that monitors and controls the battery, a central processing unit (CPU) 120 that controls the battery monitoring unit 101 as a whole, and a load circuit 130.
In such a battery monitoring system, a technique that achieves high reliability of the system is required. As such a technique, there has been a technique that adjusts, for example, a charging rate by a balance circuit, diagnoses overcharging or over-discharging to monitor the state of the battery cells, and enhance the reliability of a measuring system thus improving the reliability of the entire battery system (refer to Japanese Patent Application Laid-open No. 2010-193589).
Each of the components of the battery monitoring unit 101 in FIG. 1 is connected to a ground GND that is common to the components in the inside of the battery monitoring unit 101. When a disconnection has occurred in an electric wire (ground wire) extending to an external ground GND from a ground terminal 141 of the battery monitoring unit 101, the ground GND of each of the components such as a control IC 100 and a CPU 120 that constitute the battery monitoring unit 101 is in an isolated state. Such a state gives rise to the drawback that a reference potential is unstable, the control IC 100 and the like are abnormally operated, and the function of the battery monitoring unit 101 is eventually lost. When the function of the battery monitoring unit 101 is lost, there also gives rise to the drawback that a failure location is incapable of being identified. Also in the technique disclosed in Japanese Patent Application Laid-open No. 2010-193589, there still remains a similar drawback, and another technique has been required.